Suction roll silencer



2 Sheets-Sheet 1 Filed May 9, 1955 Oct. 28, 1958 l G. J. THlr-:ssEN2,857,823

SUCTION ROLL SILENCER Filed May 9, 1955 2 Sheets-Sheet 2 PRESSURE 3PRESSURE P5555 uRE o TIME o r/ME PR'SS URE TME' o United States Patent()SUCTION ROLL SILENCER George J. Thiessen, Ottawa, Ontario, Canada,assignor to National Research Council, Ottawa, Ontario, Canada, acorporation of Canada Application May 9, 1955, Serial No. 506,763

7 Claims. (Cl. 9253) The present invention relates to a silencer devicefor suction rolls and in particular to asilencer device for the coucused in paper machines.

In the manufacture of paper one of the problems is the removal of thewater in which the stock is carried to the machine. lt is customary todo this by the passage of the stock, supported on a screen, over vacuumor suction boxes. Some of these boxes are on the inside of rotatingdrums the low pressure being transmitted to the stock or paper byperforations in the drum surface. As these holes enter or leave thevacuum box air willv suddenly ow out of, or into, these holes in thedrum surface. This action is similar to that in a siren and results inthe high pitched scream which is so characteristic of paper machines andwhich is usually referred to as couch noise. The couch drum is, however,not the only one making this noise since any suction roll will behave inthe same way.

Because of the large amount of air flowing and the length of the drumwhich is about 20 feet, the noise intensity is very high. Sound levelsof 110 to 120 decibels are quite common (depending on the speed of themachine) in the areas near the machine commonly occupied by machineoperators. Besides the extreme annoyance caused by such noise,communication is made very diicult and what is even more importantdamage is caused to the operators hearing.

Attempts have been made in the past to reduce the noise to a level andintensity not detrimental to the machine operators. One such attempt isdisclosed in United States Patent No. 2,274,641 to E. J. Abbott and J.D. Krause which consists of a solid wedge attached to the leaving edgeof the suction or vacuum box, the upper surface of the silencer devicehaving a radius of curvature approximately equal to that of the insidesurface of the couch roll but not concentric with it. The surface of thewedge is nearly in contact at the leaving edge of the sealing strip `ofthe vacuum box, the gap between the upper surface of the wedge and thesurface of the couch roll increasing with the distance from the leavingedge.

In the operation of the silencer device above described,

it appears that the gap adjustment changes with the wear of thesilencer. Since the size of the gap is critical, the silencer is out ofcommission after a relatively short period of use. A second noteddisadvantage of the known silencer above described is that the gap isprone to become plugged with the pulp or paper being processed by thecouch roll. Unless, therefore, arrangements are made periodically toclean the gap, the silencer ceases operating after a period of time ofthe order of days.

It is an object of the present invention to provide a silencer devicefor suction rolls, in particular couch rolls, in which the disadvantagesabove mentioned would Vbe minimized and which would be adapted tooperate substantially without interruption or disturbance.

It is a further object of the invention to bring the noise emitted as aresult of the air entering the holes in ,the couch roll or drum to alevel not detrimental to rice the operators health and to the safeoperation of the couch rolls.

It is a further object of the invention to control the stream of airentering the holes in the suction or couch roll as well as to controlthe oscillations in the holes of the couch or suction roll. It isanother object of the invention to control both the stream of air andthe oscillations in adjustment with the speed at which the roll rotatesand the pressure used in the vacuum or suction box of the suction orcouch roll.

Having regard to these and other objects, the present invention will beappreciated by a study of the following specification in conjunctionwith the accompanying drawings.

In the drawings:

Figure 1 is a cross-sectional view yof one embodiment of the silencerdevice of the present invention illustrating one size, shape andlocation of the silencer device.

Figure 2 is a cross-sectional view of another embodiment of the presentinvention illustrating the silencer device of different shape andconstruction than the embodiment illustrated in Figure 1. y

Figure 3 is a graph showing the variation in time of pressure inside theholes of the suction 0r couch roll after the evacuated hole has beensuddenly exposed to atmospheric pressure.

Figure 4 shows three graphs (a), (b) and (c) showing other relationshipof the pressure inside the openings of the suction or couch roll withtime.

Referring in more details to the drawings, the silencer device of theinvention comprises a chamber 1 extending substantially the length ofthe suction or couch roll 2 and arranged next to the leaving edge 3, ofthe vacuum or suction box 4. The suction or couch roll 2 has radialholes 5 arranged along the roll, the holes being spaced at desiredintervals and extending across most of the surface of the roll 2. Thesuction or vacuum box is held against the underside of the suction orcouch roll 2 and is provided with a wide opening from which suction isapplied through the radial hole 5 to the material, such as paper, pulpor the like, travelling tangentially to the outer surface of the suctionor couch roll 2. In Figure 1 the leaving edge 3 of the vacuum `orsuction box 4 is brought in contact with the suction or couch roll 2 bymeans of a sealing strip 6. Any other suitable means of attachment ofthe vacuum or suction box to the suction or couch roll may be used. Thesilencer device comprises a chamber 1 with a narrow gap 7 cut in a strip8 attached to the top edge of the chamber 1 adjacent the leaving edge ofthe suction box 4 as shown in Figure 1. The gap 7 extends like thechamber itself substantially the length of the suction roll. To permitthe gap 7 to communicate with the chamber 1 the strip 8 is drilled withapertures 9b circumscribing an area of the strip 8 marked in Figure 1 as9. The apertures 9b circumscribing the area 9 are as close together asis permitted by the strength requirements for the strip 8. The width ofthe strip 8 is at least twice as large as the diameter of the opening 5of the couch or suction roll 2. The chamber 1 is provided in at leastone of its side walls with at least one air inlet duct 10 which isadapted to supply air at a desired rate of flow to the inside of thechamber 1.

The embodiment of the present invention shown in Figure 2, comprises agap 7 `adapted to be placed in communication with the hole 5 of thecouch roll 2, as the latter rotates, the gap in this embodiment leadingdirectly into the chamber 1, without the intermediary of a strip. As inthe embodiment illustrated in Figure 1 the chamber 1 is arranged next tothe leaving edge 3 of the vacuum or suction box 4. The enclosure 1 isprovided in at least one of its walls with at least one air inlet duct10v adapted to introduce air Vat a desired pressure .to `the enclosure 1whereby to control and regulate the pressure inside the enclosure. i

Figure 3 shows the variation of pressure `inside the opening with thetime elapsed after the opening 5 `which has been evacuated is suddenlyexposed to the atmosphere. The rate of decay of the pressure, or inother words the rate at which the oscillations in theitube tend to diedown and the pressure tends to approach atmospheric pressure, isdetermined by the rate of energy loss of the system. Frequency f ofoscillation for a given length L of the opening closed at one end, andsuddenly exposed at the open end to a pressure differentfrom thepressure inside the opening will be given approximately by theformula CfL in which c is the velocity of sound.

Figure 4 shows other forms which the relationship of pressure with timecan take inside the opening 5 depend ing on the damping. When thedamping is lowthe relationship will be that illustrated in Figure 4a,when the damping is high it will be that illustrated in Figure 4b andwhen the damping is greatly in excess of the critical value, therelationship will be that illustrated in Figure 4c.

The width of the gap 7 will be chosen for etiicient operation inrelation to the average speed at which the suction or couch roll isexpected to rotate, the effective length of the opening 5 in the suctionor couch roll 2,

and the pressure in the vacuum box. In the practice of the invention,the width of the gap 7 chosen will be very small, e. g. about 0.020 to0.030 inch but a width of up to about 0.220 inch may be used.

Since the opening 5 attains in its oscillations atmospheric pressureseveral times (the intersection points of the abscissa in Figure 3), itis, in principle, possible to close off the end at any one of thesetimes. This ensures that the average pressure is atmospheric althoughthe air is in general in a turbulent state and the opening thereforestill radiates when exposed to the open air. However, in practice, theactual opening and closing of the opening 5 does not occur suddenly andinvolves a variation of the resistance to air ow. This resistanceoperates in practice to damp out the oscillations in the opening 5.Hence no appreciable radiation will occur when the opening 5 is exposedto the open air.

ln accordance withya preferred embodiment of the invention, `the chamber1 is provided with at least one air inlet duct. The presence of the ductprevents the chamber from becoming scavenged of its air by the lowpressure openings continually arriving in it. The size of the duct ispreferably such that an air supply of the order of 2 cubic feet persecond can be supplied to the enclosure when the suction or couch rollrotates at an average speed. The air inlet duct should preferablyterminate in an acoustic filter or muier or in a chamber lined withabsorbing material to prevent the radiation from the end of the duct topenetrate into the machine room. However, even without a lter ormui-lier arrangement adequate silencing takes place with the device ofthe present invention. The chief reason for this lies in the fact that aline source will radiate in aplane at right angles to the line. Whenforced to radiate in a direction parallel to the line the acousticloading is greatly reduced and so is its acoustic eiciency. The airinlet duct or ducts is or are therefore preferably located at the endsof the chamber. Y

The silencer device of the present invention is well adapted to operatewithsuction rolls of any type used in the industry, particularly couchrolls as used in a newsprint machine in-which the couch may be 20 feetlong and about 4 feet in diameter. The shell of the .couch would beabout `1 tto `11,/2 ,inchesfthickand the` diameter of `theopenings orholes `in the couch would generally be of the order of 5A6 of an inch.Itis a particular advantage of the silencer device of the presentinvention that the paper or pulp being processed need not stay incontact with the outer surface of the suction or couch roll much longerthan usual. It is, of course, essential that the outer end of theopening 5 be closed when the opening is in contact with the gap of thesilencer enclosure. However, in view of the very small width of the gap7 which will preferably vhosen, the time of contact between the openarea the gap 7 and the open area of the opening 5 would be extremelysmall and the outer end of the opening 5 need only be closed for thatlength of time.

There will of course be an optimum width for gap 7 and the followingdiscussion will enable the most suitable width for any given operationto be chosen. By way of example, if the length of the opening 5 isapproximately 'l1/2 inch, a frequency of oscillation of the order of3000 cps. will be produced in the opening. ln this example, the time toreach atmospheric pressure for the rst time will be of the order of 0.1milliseconds. Assuming a peripheral speed of the couch of 1800 feet perminute, the drum will move, during this interval, a distance of 0.030inch. Hence this value of gap width would be approximately right.(Because of its own large diameter the hole remains in contact with thegap longer but this is approximately cancelled by the constriction ofair flow caused by the narrow gap.) Experiments on this model gavemaximum silencing for a gap width of 0.022 inch. When the pressure inthe vacuum box was ll inches of mercury below atmospheric, theresistance of the gap is not a constant but increases with theincreasing rate of flow. The width of the gap will therefore beincreased with an increase in the difference in pressure between thevacuum box and the atmosphere.

Since the gap width can only be approximately calculated it is desirableto have some control during operation. The regulation of the pressure inthe enclosure provides this control. Thus, if in the operation of thecouch roll with the silencer device of the present invention the gap 7were found to be wider than sufficient to bring the opening S toatmospheric pressure without overshooting, the enclosure would be keptat below atmospheric pressure (by simply constricting the air inletduct). Conversely, the enclosure would be kept at above atmosphericpressure if the speed of rotation of the suction or couch roll 2 washigher than usual so that the gap was in contact with the holes for anunduly short interval of time. The latter condition is not a desirableone, however, since it requires extra pumping equipment. In general itis preferred therefore to operate in a region in which constriction ofthe inlet duct can compensate for either speed changes or designtolerances.

The enclosure box of the present invention may be made of any suitablematerial, care being taken to choose the material of sound attenuationsufficient to ensure that the sound energy penetrating is negligible.

The silencer device of the present invention permits effectively tosuppress or substantially reduce the noise emitted by suction rolls orcouch rolls, substantially without interruption or disturbance. It isthus of considerable advantage both to the health of the operators andto the efficient operation of the suction or couch rolls. The gap of thesilencer enclosure does not appreciably Wear out in operation and thispermits the use of the device without the necessity for adjustment. Inview of the direction of the air flow, no appreciable clogging of thegap with shock or pump takes place. In view of the fact that the paperor pulp or the like being processed need only remain in contact withtheouter surface of the roll for very short intervals of time beyondthat spent over the suction box, the application of the silencerenclosure does not necessitate any change in the operating conditions ofthe machine.

.Itiisrintendcd thatitheipresent disclosure shouldnotbe construed in anylimiting sense other than that indicated by the scope of the followingclaims.

What I claim as my invention is:

1. A silencer device for apparatus of the type including a rotatedsuction roll having radially extending holes, and a stationary suctionbox cooperating with the inner periphery of the roll as the roll isrotated, comprising means defining a chamber extending substantially thelength of the roll and arranged next to the leaving edge of the suctionbox, said chamber having adjacent the inner periphery of the roll a gapextending substantially the length of the roll and adapted to place thechamber in communication with said holes in succession as the rollrotates, said gap being of a width not exceeding about 0.220 inch, andat least one air inlet duct in at least one of the walls of said chamberfor regulating the pressure inside said chamber.

2. A silencer device for apparatus of the type including a rotatedsuction roll having radially extending holes, and a stationary suctionbox cooperating with the inner periphery of the roll as the roll isrotated, comprising means defining a chamber extending substantially thelength of the roll and arranged next to the leaving edge of the suctionbox, said chamber having adjacent the inner periphery of the roll a gapextending substantially the length of the roll and adapted to place thechamber in communication with said holes in succession as the rollrotates, said gap being of a width not exceeding about 0.220 inch, andat least one air inlet duct in at least one of the walls of said chamberfor regulating the pressure inside said chamber whereby to compensatefor changes in the speed of the suction roll.

3. A silencer device for apparatus of the type including a rotatedsuction roll having radially extending holes, and a stationary suctionbox cooperating with the inner periphery of the roll as the roll isrotated, comprising means defining a chamber extending substantially thelength of the roll and arranged next to the leaving edge of the suctionbox and having a sealing strip in its wall facing said hole whereby tocooperate with the inner periphery of said roll, said sealing stripbeing at least twice the diameter of said hole, said chamber havingadjacent the inner periphery of said roll and arranged in said sealingstrip a narrow gap extending substantially the length of the roll andadapted to place the chamber in communication with said holes insuccession as the roll rotates, and at least one air inlet duct in atleast one of the Walls of said chamber for regulating the pressureinside said chamber.

4. A silencer device for apparatus of the type including a rotatedsuction roll having radially extending holes, and

a stationary Suction box cooperating with the inner periphery of theroll as the roll is rotated, comprising means defining a chamberextending substantially the length of the roll and arranged next to theleaving edge of the suction box and having a sealing strip in its wallfacing said hole whereby to cooperate with the inner periphery of saidroll, said sealing strip being at least twice the diameter of said hole,said chamber having adjacent the inner periphery of said roll andarranged in said sealing strip a gap extending substantially the lengthof the roll and adapted to place the chamber in communication with saidholes in succession as the roll 6 rotates, said gap being narrower thanthe width of any of said holes, and at least one air inlet duct in atleast one of the walls of said chamber for regulating the pressureinside said chamber.

5. A silencer device for Iapparatus of the type including a rotatedsuction roll having radially extending holes, and a stationary suctionbox cooperating with the inner periphrey of the roll as the roll isrotated, comprising means defining a chamber extending substantially thelength of the roll and arranged next to the leaving edge of the suctionbox and having a sealing strip in its wall facing said hole whereby tocooperate with the inner periphery of said roll, said sealing stripbeing at least twice the diameter of said hole, said chamber havingadjacent the inner periphery of said roll and arranged in said sealingstrip a gap extending substantially the length of the roll and adaptedto place the chamber in communication with said holes in succession asthe roll rotates, said gap being narrower than the width of any of saidholes, and at least one air inlet duct in at least one of the walls ofsaid chamber for regulating the pressure inside said chamber whereby tocompensate for changes in the speed of the suction roll.

6. A silencer device for apparatus of the type including a rotatedsuction roll having radially extending holes,

and a stationary suction box cooperating with the inner periphery of theroll as the roll is rotated, comprising means defining a chamberextending substantially the length of the roll and arranged next to theleaving edge of the suction box, said chamber having adjacent the innerperiphery of the roll a narrow gap extending substantially the length ofthe roll and adapted to place the chamber in communication with saidholes in succession as the roll rotates, said gap being narrower thanany of said radially extending holes of the suction roll, and at leastone air inlet duct in at least one of the walls of said chamber forregulating the pressure inside said chamber.

7. A silencer device for apparatus of the type including a rotatedsuction roll having radially extending holes, and a stationary suctionbox cooperating with the inner periphery of the roll as the roll isrotated, comprising means defining a chamber extending substantially thelength of the roll and arranged next to the leaving edge of the suctionbox, said chamber having adjacent the inner periphery of the roll anarrow gap extending substantially the length of the roll and adapted toplace the chamber in communication with said holes in succession as theroll rotates, said gap being of a width between about 0.020 and 0.030inch, and at least one air inlet duct in at least one of the walls ofsaid chamber for regulating the pressure inside said chamber.

References Cited in the tile of this patent UNITED STATES PATENTS1,091,941 Marx Mar. 31, 1914 1,581,656 Monaghan Apr. 20, 1926 2,107,812Berry et al. Feb. 8, 1938 2,274,641 Abbott et al Mar. 3, 1942 2,290,777Street July 21, 1942 FOREIGN PATENTS 677,526 Germany June 27, 1939

